Field of the Invention
This invention relates to: an image reading apparatus that can acquire each of detection results of a first image detecting section which reads an image on a transfer medium and has high failure detection accuracy, and a second image detecting section which reads the image and has high color detection accuracy; an image forming apparatus; an image forming system; an image forming method; and a non-transitory computer-readable recording medium which stores an image forming control program therein.
Description of the Related Art
In an image forming apparatus such as a printer and a multifunctional machine, an image forming apparatus is conventionally known which prints a color patch, detects a patch of the output image by a color concentration sensor and the like, compares the detected patch with original print data, corrects printing density and the like when a difference occurs between the patch and the data, and forms an image, in order to enhance an image quality of an output image.
The size of the patch which is printed on paper in such an image adjustment mode is preferably controlled to be a small size as much as possible in a paper travel direction, in order to reduce paper for adjustment.
In recent years, in order to reduce image adjustment time period and the like in an image forming apparatus for further enhancing the image quality, the image forming apparatus also has appeared that is provided with an image reading apparatus which mounts an in-line image scanner. This image scanner can be used for correcting misalignment of the front and back of the paper, image density, tint and the like of the output image in real time. A line sensor is widely used in the image scanner, which uses CCD or CIS as an imaging element.
However, the image scanner is not excellent in color reproducibility, and accordingly has also such a feature that colorimetric accuracy cannot be guaranteed.
Then, if the image scanner mounts an in-line colorimeter for correctly measuring the tint and correcting an absolute color into print data, the colorimeter can contribute to a further reduction of the adjustment time period. A spectral colorimeter can be used for the colorimeter. The spectral colorimeter is an instrument which exposes a color patch to light of an LED or the like, disperses reflected light with a diffraction grating, collects the dispersed light with a CMOS sensor or the like, and derives the result as a hue expressed by L*a*b* or the like. The line sensor can detect the patch on the whole surface of the paper. Accordingly, if a correlation is taken between a true tint acquired by the colorimeter and color data acquired by the line sensor, and the line sensor is thereby corrected, it also becomes possible to form the patch on the whole surface of the paper and can also save the paper for adjustment.
Specifically, it is considered to read out the image by the line sensor, and periodically calibrate the line sensor by the spectral colorimeter of which the colorimetry accuracy is guaranteed, or the like.
In addition, it is effective to mount the colorimeter, also in managing the absolute color and tuning the print data. In order to accurately detect the hue, though the method includes repeated measurement with the spectral colorimeter, a predetermined detection time period is necessary, and when the spectrum is detected in multiple times and respective results are totalized, the accuracy can be thereby more enhanced.
When exposing the patch on a moving sheet of paper to light four times, receiving reflected light and integrating the light, for instance, and outputting the hue, the image reading apparatus accumulates the reflected light, as first measurement in a first colorimetric area, second measurement in a second colorimetric area, and so on, as is shown in FIG. 8. A portion which straddles a boundary between the first colorimetric area and the second colorimetric area is determined by an aperture size (visual field=spot) of the colorimeter. For instance, the exposure to light for 4 ms and the acquisition of spectral reflected light are repeated four times, and the values are averaged. When the colorimetry of the first colorimetric area has ended, the colorimetry of the second colorimetric area results in starting.
When the colorimeter concentrates on acquiring the hue and the image forming apparatus provides a signal of the colorimetry timing which corresponds to the patch position, it becomes thereby unnecessary to identify a boundary between different patches and it also becomes possible to keep the patch size small.
By the way, when the colorimeter measures the color, in the case where there are inconsistencies in density, dirt, a scratch and the like in the patch, there is a problem that the colorimeter cannot correctly measure the color and be calibrated.
In Japanese Patent Laid-Open No. 2007-30340, an image forming apparatus reads out an image by a sensor device which uses the colorimeter, a densitometer or the like, and adjusts the density of the toner image which is formed by an image forming unit according to the readout result, but when there is dirt on a part of the patch, makes it possible to form a patch image in a region other than the region, read out the patch image and adjust the output density.
In addition, in Japanese Patent Laid-Open No. 2009-124458, the method has a step of predicting whether or not there is abnormality in the patch for colorimetry, from a colorimetric result of an appropriate patch, and deriving the prediction value, and when the prediction value has exceeded a certain threshold value, makes it possible to report that the patch is not appropriate.
As has been described above, a line sensor which uses CCD (Charge Coupled Device) or CIS (Contact Image Sensor) as an imaging element is widely used in reading the image. The line sensor is suitable for reading at high speed, can read out an image fixed on transfer paper just at a conveyance speed of a fixed portion, can check color reproducibility, and inspect a printing position and the like. The line sensor can detect an image with a unit of μm, and as a result of having analyzed the image, can correctly specify a position of an abnormal image of a mixed foreign matter or the like.
On the other hand, in the spectral colorimeter, in order to enhance colorimetry accuracy, the colorimeter averages colorimetric results in the area containing several points and calculates the hue; and accordingly is excellent in a measurement accuracy of the color. However, the colorimeter needs to make the quantity of the integrated light per one patch constant, and when reading out the patch at the same conveyance speed as that of the line sensor, needs to elongate the patch length. However, when the patch length becomes long, the number of sheets of a chart necessary for calibration increases, and there is a problem that waste paper results in being produced per one calibration. In addition, the colorimeter is not suitable for determining an image failure.
However, as has been described above, when there is a failure portion in the patch, it becomes difficult to appropriately calibrate the line sensor on the basis of a result of reading by the colorimeter.
In Japanese Patent Laid-Open No. 2007-30340, the image forming apparatus needs to form a patch in another place so as to avoid an area of an abnormal image, and move the place for measuring the color there; and accordingly results in needing a movement mechanism for carrying the colorimeter to a matching place every time, and causing an increase of the cost. In addition, the image forming apparatus is an apparatus which changes the patch position to another place based on a premise that the area of the abnormal image is specified and is stably abnormal, and cannot cope with an accidentally abnormal image, dirt and the like.
In addition, in Japanese Patent Application Laid-Open No. 2009-124458, the method determines a predicted value, based on the colorimetric result of a patch in a correct state, and when the value is different from the predicted value, determines that the patch is not appropriate, and accordingly firstly needs to measure the color of the patch in the correct state; and when the colorimetry by the line sensor is not performed with reliability, the predicted value also becomes inappropriate. In addition, there is a problem that the abnormality cannot be surely eliminated, considering that the predicted value contains a prediction error. Furthermore, when the patch becomes inappropriate, the present patch becomes incapable of being used, and then the patch needs to be printed again, which causes a problem that paper for adjustment results in being wasted.